Wellbores are created for a variety of purposes, including exploratory drilling for locating underground deposits of different natural resources, mining operations for extracting such deposits, and construction projects for installing underground utilities. A common misconception is that all boreholes are vertically aligned with the drilling rig; however, many applications require the drilling of boreholes with vertically deviated and horizontal geometries. A well-known technique employed for drilling horizontal, vertically deviated, and other complex boreholes is directional drilling. Directional drilling is generally typified as a process of boring a hole which is characterized in that at least a portion of the course of the bore hole in the earth is in a direction other than strictly vertical—i.e., the axes make an angle with a vertical plane (known as “vertical deviation”), and are directed in an azimuth plane.
Directional drilling typically requires controlling and varying the direction of the drill string and drilling device during drilling. Oftentimes the goal of directional drilling is to reach a position within a target subterranean destination or formation. Various options are available for providing steering capabilities to a drilling device for controlling and varying the direction of the wellbore. In directional drilling applications, for example, one option is to attach a bent-housing or a bent-sub downhole drilling motor to the end of the drilling string as a steering tool.
Directional drilling may also be accomplished with a “rotary steerable” drilling system wherein the entire drill pipe string is rotated from the surface, which in turn rotates the bottomhole assembly, including the drilling bit, connected to the end of the drill pipe string. In a rotary steerable drilling system, the drilling string may be rotated while the drilling tool is being steered either by being pointed or pushed in a desired direction (directly or indirectly) by a steering device. Some rotary steerable drilling systems include a component which is non-rotating relative to the drilling string in order to provide a reference point for the desired direction and a mounting location for the steering device(s).
As a third option, directional drilling may be accomplished using a combination of both rotary steerable drilling and sliding drilling. Rotary steerable drilling will typically be performed until such time that a variation or change in the direction of the wellbore is desired. Rotation of the drill pipe string is then stopped and sliding drilling, through use of the downhole motor, is commenced. Although the use of a combination of sliding and rotary drilling may permit satisfactory control over the direction of the wellbore, many of the problems and disadvantages associated with sliding drilling are still encountered.
It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.